This invention relates to load cells and more particularly to a moment-insensitive load cell enclosed or hermetically sealed by means of an expansible convoluted enclosure such as a bellows.
A single or multiple beam load cell may be compensated for the effects of torsional forces produced by off-center applications of load by, for example, the methods taught in U.S. Pat. Nos. 4,380,175 and 4,453,609 issued to Neil C. Griffen and assigned to the Assignee of the present invention. A load cell compensated for such off-center loading effects is known as a "Moment-Insensitive Load Cell" (hereinafter MILC). The methods of compensation taught by Griffen makes it desirable that the errors due to off-center loading be linear as the point of off-center load application is moved transversely from one to the other side of the load cell.
Recently, it has become desirable for some applications to hermetically seal the central portions of the MILC bearing the strain gages or other force transducers. A bellows has been found suitable for the purpose, enclosing the load cell so that its convolutions encircle the longitudinal axis of the load cell beam or beams. A narrower neck portion at each end of the bellows is welded to the load cell. With this orientation, the bellows, because of the convolutions, is weak in the direction of load cell bending or flexure and has no significant effect on the load cell output.
More recently, however, it has been discovered that such hermetically sealed load cells have been very difficult to compensate for transverse off-center loading.